One more factor to consider--->
If you DO miss your Southwest flight, you can utilize their "flat tire" rule to standby on a later flight to your destination. However, if your destination is on a longer-haul Southwest flight or a flight to Hawaii or Las Vegas, you may be in trouble because these flights are often booked high or sold out. Shorter hauls (except LAS) are not as impacted, based on my experience and a discussion with a flight attendant on her observations of load factors nowadays. Note that passengers with status with Southwest are given standby priority on Southwest.

For a preview of what alternate flights might be available for standby travel, try booking 8 passengers on a one-way flight to your desired destination for today's date on the Southwest booking site. For example, right now the only nonstop flight with seats available from LAX-LAS today departs 14 hours from now. There are earlier flights with connections, but I am unsure of Southwest's policy on alternate routing standby passengers who have missed their original flight.